Production of wire rod and wire



PRODUCTION OF WIRE ROD AND WIRE Peter Bardenheuer, Altena, Gustav Wehner, Mainz- Gustavsburg, and Paul Klare, Frankfurt am Main, Germany, assignors to Vereinigte Deutsche Metallwerlte Aktiengesellschaft, Frankfurt am Main, Germany, a corporation of Germany No Drawing. Application February 20, 1952, Serial No. 272,696

Claims priority, application Germany March 7, 1951 6 Claims. (Cl. 29-547) The present invention relates to an improved process for the production of metal stock used in the production of wire and more particularly to the production of copper wire rods and wire.

The starting material employed for the production of rolled copper wire rods from which copper wire is drawn is customarily the so-called cast wire bars having crosssections varying from about 3 /2 x 3 /2 to 4 x 4, and which weigh about 220 to 330 pounds. As the wire rods are normally about A inch in diameter, the reduction of the wire bars to the wire rods does effect a certain amount of working of the metal. Nevertheless, the smooth copper wire drawn from wire rods produced from such cast wire bars do not meet many requirements. Wire drawn from wire rods produced from horizontally cast wire bars often exhibit many surface flaws such as cracks and scales which are evidently engendered either directly by the cupro-us oxide which occurs in the zone below the surface of the cast wire bar which has solidified in contact with air, or by reaction of such cuprous oxide with hydrogen taken up by the bars during heating.

Other surface flaws which occur in wire drawn from rolled wire rods obtained from either vertically or horizontally cast wire bars can lead to difiiculties, especially in the production of copper wire which is to be insulated by a thin lacquer coating. A portion of these flaws can be traced back to the following cause: as is known, the crystals forming the metallic crystal structure possess different mechanical properties in the direction of their various axes and, consequently, different resistances to deformation. For example, the tensile strength of a copper crystal in its axial direction is 35 kg./cm. whereas transverse thereto, it is only 14.6 kg./cm. and in aluminum the tensile strengths are respectively 11.5 kg./cm. and 6.1 kg./cm. The substantial difference in deformability caused by the different strengths is especially noticeable in the crystals which lie free upon the surface of the metal and the more so, the coarser such crystals are. In cast copper wire bars the individual crystals are extraordinarily coarse and have a grain size between several mm. to several cm.", on the other hand, the grain size of a well annealed rolled copper amounts to only about 100 and, consequently, the grain size of the cast wire bars is about 10 to 10 larger than in rolled copper. Only with thorough working with large reduction in cross-section are the coarse grains shattered.

In the initial phases of rolling copper containing the aforementioned large crystals, the crystals which are so oriented that they are most easily deformed in the direction vertical to the surface, will extend relatively further out of the surface than the crystals differently orientated. This is noticeable by the roughening of the surface and in further rolling the extending crystals often are pushed over the lower lying crystals whereby the oxide skin is covered in spots. The enveloped oxides are only incompletely removed during pickling and metal scales remain nited States Patent Pal-tented June 12, 1956 loosely attached through one of their sides to the wire rods and such scales are still present in the drawn wire. Such scales are often so numerous that a lacquer coating applied on thin copper wires will easily become detached along with such scales.

It has already been proposed to remove the unsound surface by scraping operations to avoid such difficulties. Such scraping operations are usually in conjunction with the drawing operations and are very costly. Furthermore, they produce a considerable quantity of finely divided metal the reuse of which is troublesome and accompanied by substantial loss of metal.

It has also been proposed to produce the wire rods by extrusion from round billets in order to avoid warm rolling. The wire drawn therefrom does have a smooth surface adapted to lacquering, but this process is very expensive and the cold drawing must initially be carried out very carefully with only small reductions in size.

It is an object of the invention to provide a process for the economical production of non-ferrous metal stock such as wire rod for the production of wire substantially avoiding the aforementioned difliculties.

It is a further object of the invention to provide a process for the production of copper wire rods for the production of copper wire of improved conductivity.

In accordance with the invention, it has been unexpectedly discovered that wire rods and similar products can be simply and economically produced which are suitable for the production of copper wire which has excellent surface characteristics, by employing cast ingots the cross-section of which is at least 64 square inches (about 40,000 mm?) as the starting materials instead of the usual cast wire bars which have a cross-section of between about 12 and 16 square inches. The cross-section of such ingots is first reduced by rolling, forging or pressing to a cross-section of about 12 to 16 square inches and then preferably after dividing the resulting bar and reheating to rolling temperature such bars are rolled to wire rod. The rolling of the cast ingot to the wire rod can also be carried out in the same heat. The reduction in crosssection of the cast ingots to the wire rods in accordance with the invention amounts to at least 1260:1, whereas the reduction in size effected previously from the cast wire bars to the wire rods was only about 245:1 to 326: 1.

Wire is produced from the hot rolled wire rods obtained according to the process of the invention in the normal manner by cold drawing. The unsound surface layer which is initially formed during the hot rolling of the billets becomes so thin because of the extreme reduction of the cross-section thereof, that it completely oxidizes at the rolling temperatures or during reheating of the billets for rolling so that it is completely removed along with the mill scale during pickling.

The wire rod produced by the process according to the invention diflfers from those produced by the usual processes in its excellent surface character. Already after pickling and the first drawing operation the surface is completely smooth and flawless and, consequently, the copper wire resulting from the first drawing operation as well as subsequent drawing operations can already be employed in the production of excellent lacquered wire. The surface character of the wires produced from wire rods according to the invention is even superior to that of wire obtained from rods produced by the much more costly extrusion process.

The wire rod produced according to the invention is furthermore exceptionally soft and ductile and, consequently, its resistance to deformation and its cold working hardening is substantially lower than of wire rod of the same composition and size produced by the prior customary processes. It was also unexpectedly found that copper wire rods produced according to the invention can be drawn to a diameter of 0.05 mm. and less without danger of premature breaking of the wire.

Furthermore, copper wire drawn from wire rod produced according to the invention has a remarkably high electrical conductivity. For example, a wire produced from copper which was smelted from scrap in a refining oven and still contained 0.018% of oxygen has a conductivity of more than 58 S. E. which is a value which previously could only be obtained with wire produced from cathode copper.

The following example will serve to illustrate the process according to the invention.

Example A copper ingot weighing about 3.5 tons having an average cross-section of 18.4 x 18.4 inches was hot rolled in a steel blooming mill to a billet having a 3.4 X 3.4 inch cross-section. The billet was then subdivided into bars and these bars were then reheated and hot rolled in a wire rod rolling mill to wire rod of about inch diameter. The rolling temperatures employed were those customarily employed in hot working copper, namely, between 1300 and 1650 F. The resulting wire rods were pickled with dilute sulfuric acid to remove the scale and then cold drawn to copper wire in the customary manner.

The reduction in cross-section from the starting ingot to the A1 inch wire rod was 697021 and investigations of wire drawn from such wire rods of a diameter of 1.4 mm. and much smaller diameters such as 0.05 mm. indicate that the surface character thereof is considerably better than that of wire drawn from wire bars produced in the previously customary manner.

We claim:

1. A process for the production of electrical conductor copper wire which comprises hot working a cast ingot consisting of copper to form a wire rod, the original crosssection of said cast ingot being selected at least 1.260 times the cross-section of the wire rod produced therefrom, pickling said wire rod to remove any adherent scale, and cold drawing such rod to form wire.

2. The process of claim 1 in which said wire rod is cold drawn to form wire having as a maximum a diameter of 0.05 mm.

3. The process of claim 1 comprising in addition lacquering such wire.

4. The process of claim 1 in which said cast ingot consisting of copper is hot rolled to form the wire rod.

5. The process of claim 4 in which said wire rod is cold drawn to form wire having as a maximum a diameter of 0.05 mm.

6. The process of claim 4 comprising in addition lacquering such wire.

References Cited in the file of this patent UNITED STATES PATENTS Re. 7,913 ONeill Get. 16, 1877 662,247 Vinton Nov. 20, 1900 1,901,920 McMullan Mar. 21, 1933 2,063,677 Hughes et a1 Dec. 8, 1936 2,074,712 Tross Mar. 23, 1937 2,257,535 Rohn Sept. 30, 1941 2,260,351 Strawn Oct. 28, 1941 2,260,914 MeGar Oct. 28, 1941 2,333,238 Finnie Nov. 2, 1943 

1. A PROCESS FOR THE PRODUCTION OF ELECTRICAL CONDUCTOR COPPER WIRE WHICH COMPRISES HOT WORKING A CAST INGOT CONSISTING OF COPPER TO FORM A WIRE ROD, THE ORIGINAL CROSSSECTION OF SAID CAST INGOT BEING SELECTED AT LEAST 1260 TIMES THE CROSS-SECTION OF THE WIRE ROD PRODUCED THEREFROM, PICKLING SAID WIRE ROD TO REMOVE ANY ADHERENT SCALE, AND COLD DRAWING SUCH ROD TO FORM WIRE. 